The present invention relates generally to transistor switches and more particularly to noninverting transistor switches.
Noninverting transistor switches are well known in the art and widely used. In the past, such switches have contained at least four terminals, one terminal being used as an input, another terminal being used to connect the device to a load, another terminal being used for ground or return and the last terminal being connected to a power supply used to provide a "second" inversion.
Inverting three terminal transistor switches are also well known in the art.
In U.S. Pat. No. 4,266,100 to Hopper et al. there is disclosed a monolithically integrated semiconductor circuit, provided for coupling arrangements having symmetrical cross points, comprising two through switching NPN transistors, and a composite circuit for switching through the switching transistors. The composite circuit includes a double collector PNP transistor, with one collector connected to the base of a first NPN transistor and the other collector connected to the base of a second NPN transistor. The emitter of the double collector transistor is connected to the collector of both NPN transistors and also, via a first resistor to a voltage source. The base of the double collector transistor is connected, via a component causing a constant drop in voltage, to the voltage source, and also via a second resistor, to a trigger stage. The emitters of the NPN transistor are connected, respectively to the bases of the two through switching transistors.
In U.S. Pat. No. 4,307,298 to El Hamamsy et al. there is disclosed an optically toggled bilateral field effect transistor switch having a low leakage current is described. A high impedance path and, therefore, a low leakage current, is provided by a photovoltaically controlled field effect transistor.
In U.S. Pat. No. 4,390,790 to Rodriquez there is disclosed a solid state optically coupled power switch with light induced or modified voltage applied or removed at one or more MOSFET gate and source electrode pairs to shift each MOSFET between its high and low impedance states and in various circuit arrays for ac or dc switching and/or cross points switching or mechanical Form C relay substitution or other purposes.
In U.S. Pat. No. 4,410,809 to Puruichi et al. there is disclosed a disclosure related to a gate driving circuit for a depletion type, static induction transistor, including a capacitor coupled between the emitters of complementary-connected NPN and PNP transistors and the SIT gate, high value resistor parallel-connected to a series connection of a diode and a resistor between the SIT gate, and a negative gate voltage source.
In U.S. Pat. No. 4,849,683 to Flolid there is disclosed a lamp driver circuit for supplying and controlling power to a lamp from a power supply subject to voltage variations. A semiconductor switch is disposed in series with the lamp and a current sensing resistor. A capacitor integrates the lamp current during ON time of the switch and power supply voltage during OFF time. A voltage comparator with hysteresis responds to the capacitor voltage to control the conductive state of the switch. Above a nominal supply voltage, the driver circuit begins to pulse width modulate the power supplied to the lamp with a duty cycle inversely proportional to the square of the supply voltage to maintain constant power to the lamp. As the supply voltage rises above a second predetermined level, the driver circuit ceases to supply power.
Other known references of interest include the 1986 Linear Data Book by Linear Technology, pp. 2-170 and 2-171; Feb. 1990 QST pp. 24 through 27; the Feb. 1989 edition of PCIM pp. 22 through 27, and Blicher A., Field Effect and Bipolar Power transistor Physics, New York, Academic Press, 1981 Chapters 11 and 13.
It is an object of this invention to provide a new and improved transistor switch.
It is another object of this invention to provide a transistor switch that is noninverting.
It is still another object of this invention to provide a transistor switch that is noninverting and which contains only three terminals.
It is yet still another object of this invention to provide a noninverting transistor switch which does not include an additional power supply for obtaining a second inversion.
It is a further object of this invention to provide a three terminal transistor switch which is normally closed.
It is still a further object of this invention to provide a transistor switch which does not require a local or a wired-in power supply.